Laboratory reference values are essential for the interpretation and validation of clinical results. These values are often based on urban populations, disregarding physiological variations due to geographic, environmental, ethnic, cultural, and socioeconomic factors. Amazonian riverside communities are a neglected population group in epidemiological and laboratory studies, with significant specificities that can influence hematological parameters.

To establish reference values for blood count parameters in an Amazonian riverside population.

This observational, cross-sectional study, with randomized sampling, was conducted in July 2025, involving healthy adults (12 to 88 years old), non-pregnant, without ongoing medication use and recent infections, living in 9 communities bordering the Solimões and Purus rivers (Amazonas, Brazil). Venous blood was processed (within 10 minutes of puncture) on an automated hematology analyzer (AMA H-6028, AMA Medical) after rigorous quality control. Statistical analysis demonstrated low data dispersion, suggesting sample consistency.

219 samples were evaluated, 54 and 165 from male and female patients, respectively. Male patients presented: Leukocytes: 6.55 ± 1.87 × 10³/µL; Neutrophils: 62.36 ± 8.80%; Lymphocytes: 26.61 ± 7.49%; Monocytes: 5.15 ± 0.80%; Eosinophils: 5.63 ± 5.08%; Basophils: 0.25 ± 1.87%; Erythrocytes: 5.02 ± 0.32 × 10⁶/µL; Hemoglobin: 14.95 ± 1.07g/dL; Hematocrit: 43.09 ± 2.65%; MCHC: 34.54 ± 0.79g/dL; MCH: 29.79 ± 1.45pg; MCV: 86.25 ± 3.52 fL; RDW: 12.93 ± 0.48%; Platelets: 275.69 ± 53.90 × 10³/µL. The values for females were: Leukocytes: 7.59 ± 2.04 × 10³/µL; Neutrophils: 63.30 ± 9.40%; Lymphocytes: 28.47% ± 8.61; Monocytes: 4.54 ± 0.53%; Eosinophils: 3.49 ± 3.59%; Basophils: 0.15 ± 0.15%; Erythrocytes: 4.54 × 10⁶/ µL ± 0.37; Hemoglobin: 13.34 ± 1.01g/dL; Hematocrit: 39.06 ± 2.58%; MCHC: 34.05 ± 0.69 g/dL; MCH: 29.49 ± 1.76 pg; MCV: 86.54 ± 4.13fL; RDW: 12.46 ± 0.52%; Platelets: 319.92 ± 70.01 × 10³/µL.

Most hematologic values were within the reference ranges suggested by the Brazilian Society of Clinical Analysis (SBAC). Leukocyte counts were normal, and the leukocyte differential remained within reference ranges, with only slight eosinophilia in men, possibly associated with endemic parasitic infections or allergic processes. Erythrograms showed normal mean erythrometry, hemoglobin, and hematocrit values, with higher values in men due to androgenic steroids. Hematimetric indices indicated a normocytic and normochromic erythrocyte profile, with low anisocytosis, suggesting the absence of significant deficiency anemias. Platelet counts were within normal limits, with a slightly higher mean in women. The reference values reflect the hematological profile of an Amazonian population, consistent with the values established by the SBAC, demonstrating that despite the distinct lifestyle characteristics of urban populations, hematological values are consistent. The importance of regional contexts in the interpretation of laboratory tests is emphasized, promoting greater diagnostic accuracy and equity in healthcare. Regional reference values can contribute to improving care in remote areas and strengthening local evidence-based medicine.